Camber is a significant defect that occurs in hot steel slabs or strips when being rolled in mills or manufacturing plants. It is a straightness defect characterized by longitudinal curvature in the strip. Camber is caused by the lateral unstable movement of the strip in work rolls that leads the strip to curve towards a side. This defect creates clogging in the finishing stages and severely affects the quality of the produced strip which results in wastage of the produced steel.
In practice, the camber is manually eliminated by stand leveling the work rolls which makes the strip to come back in the center of the rolls. Steering control systems are system which automatically detects camber and takes measures to bring the strip back to the centerline. However, these systems rely on indirect measures such as width measurement sensors to capture the edge profile and therefore camber.
In current manufacturing practice, camber defect is qualitatively identified by the human operator and the steering control of the work rolls is adjusted to bring the strip back to the center line of the rolls. Quantitatively, camber in the defected slab can be measured by placing two magnets in the strip across the cambered portion and attach them with a string, thereby measuring the distance between the string and the concave edge. Automatic steering control systems have been developed to automate the steering process. Most of these attempts to measure the camber through indirect measures, such as placing sensors along the way of the movement of strip to get the edge profile.
Camber measurement has to be a real-time process in which the camber value is fed into the steering control to adjust the rolls for correction. So, it has to be automatic, robust, accurate, computationally inexpensive and cheap. Manual measurement is not an option to be considered as it ends up wasting good amount of produced steel. Today, manufacturing industry is targeting zero wastage policy and automation is the most sought after option. The manual technique of “magnet and string” camber measurement cannot be applied in the real-time as the steel strip is of very high temperature.
Automatic steering control systems which use sensors for detecting camber are costly and yield inaccurate measurement as they follow indirect means to measure it. Computer vision based camber measurement is considered as cheap and effective option. Few methodologies have been developed but they are either computationally expensive or not reliable. Since the processing of image frames for measuring camber has to happen on-line, lots of optimization needs to be done to reduce the computation.